OFDM (orthogonal frequency division multiplexing) is a special multi-carrier transmission technology. It separates a wide transmission bandwidth into multiple mutually orthogonal subcarriers for transmitting data in parallel.
In an OFDM system, to schedule radio resources, the base station needs to obtain the downlink channel state information of the UE. Generally, the information is generally obtained after the UE (user equipment) measures and reports it. The measuring and reporting method mainly includes: The base station transmits a reference signal; and the UE uses the received reference signal to measure and obtain the downlink channel state information: and then the UE feeds back the measured downlink channel state information to the base station. The base station performs radio resource scheduling for the received downlink channel state information that is fed back by each UE, and decides how to allocate limited time and frequency resources to each UE, so as to maximize the usage of radio resources.
However, in the process of developing the present invention, the inventor finds that in an MIMO (multiple input multiple output) system, the base station has multiple antenna ports, and each antenna port has a reference signal to be sent. The UE needs to measure channel state information of all antenna ports, and feeds back the information to the base station. Therefore, the overhead of measurement and feedback is huge.